Horton

Re: AIO v2.5

Jakub Wartak <jakub.wartak@enterprisedb.com>

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From: Jakub Wartak <jakub.wartak@enterprisedb.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>
Date: 2025-03-07T10:21:09Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. aio: Fix assertion, clarify README

  2. aio: Fix reference to outdated name

  3. aio: Fix possible state confusions due to interrupt processing

  4. aio: Improve debug logging around waiting for IOs

  5. aio: Fix crash potential for pg_aios views due to late state update

  6. Increase BAS_BULKREAD based on effective_io_concurrency

  7. localbuf: Add Valgrind buffer access instrumentation

  8. aio: Make AIO more compatible with valgrind

  9. aio: Avoid spurious coverity warning

  10. tests: Fix incompatibility of test_aio with *_FORCE_RELEASE

  11. tests: Cope with WARNINGs during failed CREATE DB on windows

  12. aio: Add errcontext for processing I/Os for another backend

  13. aio: Add README.md explaining higher level design

  14. aio: Minor comment improvements

  15. aio: Add test_aio module

  16. aio: Add pg_aios view

  17. docs: Add acronym and glossary entries for I/O and AIO

  18. Enable IO concurrency on all systems

  19. read_stream: Introduce and use optional batchmode support

  20. docs: Reframe track_io_timing related docs as wait time

  21. bufmgr: Use AIO in StartReadBuffers()

  22. bufmgr: Implement AIO read support

  23. aio: Add WARNING result status

  24. Let caller of PageIsVerified() control ignore_checksum_failure

  25. pgstat: Allow checksum errors to be reported in critical sections

  26. Add errhint_internal()

  27. localbuf: Track pincount in BufferDesc as well

  28. aio, bufmgr: Comment fixes/improvements

  29. Fix mis-attribution of checksum failure stats to the wrong database

  30. aio: Implement support for reads in smgr/md/fd

  31. aio: Add io_method=io_uring

  32. aio: Add liburing dependency

  33. aio: Rename pgaio_io_prep_* to pgaio_io_start_*

  34. aio: Pass result of local callbacks to ->report_return

  35. aio: Be more paranoid about interrupts

  36. Redefine max_files_per_process to control additionally opened files

  37. aio: Change prefix of PgAioResultStatus values to PGAIO_RS_

  38. bufmgr: Improve stats when a buffer is read in concurrently

  39. aio: Add io_method=worker

  40. aio: Infrastructure for io_method=worker

  41. aio: Add core asynchronous I/O infrastructure

  42. aio: Basic subsystem initialization

  43. tests: Expand temp table tests to some pin related matters

  44. localbuf: Introduce FlushLocalBuffer()

  45. localbuf: Introduce TerminateLocalBufferIO()

  46. localbuf: Fix dangerous coding pattern in GetLocalVictimBuffer()

  47. localbuf: Introduce StartLocalBufferIO()

  48. localbuf: Introduce InvalidateLocalBuffer()

  49. Allow lwlocks to be disowned

  50. Make jsonb casts to scalar types translate JSON null to SQL NULL.

  51. bufmgr/smgr: Don't cross segment boundaries in StartReadBuffers()

  52. Use aux process resource owner in walsender

  53. bufmgr: Return early in ScheduleBufferTagForWriteback() if fsync=off

On Thu, Mar 6, 2025 at 2:13 PM Andres Freund <andres@anarazel.de> wrote:

> On 2025-03-06 12:36:43 +0100, Jakub Wartak wrote:
> > On Tue, Mar 4, 2025 at 8:00 PM Andres Freund <andres@anarazel.de> wrote:
> > > Questions:
> > >
> > > - My current thinking is that we'd set io_method = worker initially - so we
> > >   actually get some coverage - and then decide whether to switch to
> > >   io_method=sync by default for 18 sometime around beta1/2. Does that sound
> > >   reasonable?
> >
> > IMHO, yes, good idea. Anyway final outcomes partially will depend on
> > how many other stream-consumers be committed, right?
>
> I think it's more whether we find cases where it performs substantially worse
> with the read stream users that exist.  The behaviour for non-read-stream IO
> shouldn't change.

OK, so in order to to get full picture for v18beta this would mean
$thread + following ones?:
- Use read streams in autoprewarm
- BitmapHeapScan table AM violation removal (and use streaming read API)
- Index Prefetching (it seems it has stalled?)

or is there something more planned? (I'm asking what to apply on top
of AIO to minimize number of potential test runs which seem to take
lots of time, so to do it all in one go)

> > So, I've taken aio-2 branch from Your's github repo for a small ride
> > on legacy RHEL 8.7 with dm-flakey to inject I/O errors. This is more a
> > question: perhaps IO workers should auto-close fd on errors or should
> > we use SIGUSR2 for it? The scenario is like this:
>
> When you say "auto-close", you mean that one IO error should trigger *all*
> workers to close their FDs?

Yeah I somehow was thinking about such a thing, but after You have
bolded that "*all*", my question sounds much more stupid than it was
yesterday. Sorry for asking stupid question :)

> The same is already true with bgwriter, checkpointer etc?

Yeah.. I was kind of looking for a way of getting "higher
availability" in the presence of partial IO (tablespace) errors.

> > pg_terminate_backend() on those won't work. The only thing that works seems
> > to be sending SIGUSR2
>
> Sending SIGINT works.

Ugh, ok, it looks like I've been overthinking that, cool.

> > , but is that safe [there could be some errors after pwrite() ]?
>
> Could you expand on that?

It is pure speculation on my side: well I'm always concerned about
leaving something out there without cleanup after errors and then
re-using it for something else much later, especially on edge-cases
like NFS or FUSE. In the backend we could maintain some state, but
io_workes are shared across backends. E.g. some pwrite() failing on
NFS, we are not closing that fd, and then reusing it for something
else much latter for different backend (although AFAIK close() does
not guarantee anything, but e.g. it could be that some inode/path or
something was simply marked dangling - the fresh pair of
close()/open() could could could return error, but here we would just
keep on pwriting() there?).

OK the only question remains: does it make sense to try something like
pgbench on NFS UDP mountopt=hard,nointr + intermittent iptables DROP
from time to time , or is it not worth trying?

> > With
> > io_worker=sync just quitting the backend of course works. Not sure
> > what your thoughts are because any other bgworker could be having open
> > fds there. It's a very minor thing. Otherwise that outage of separate
> > tablespace (rarely used) would potentially cause inability to fsck
> > there and lower the availability of the DB (due to potential restart
> > required).
>
> I think a crash-restart is the only valid thing to get out of a scenario like
> that, independent of AIO:
>
> - If there had been any writes we need to perform crash recovery anyway, to
>   recreate those writes
> - If there just were reads, it's good to restart as well, as otherwise there
>   might be pages in the buffer pool that don't exist on disk anymore, due to
>   the errors.

OK, cool, thanks!

-J.